Which of the following is NOT a common type of aggregate used in base layers?

The correct choice identifies wood as not being a common type of aggregate used in base layers. In construction and engineering, base layers are typically composed of durable and granular materials that provide a strong foundation for roads, pavements, and other structures.

Materials like crushed stone, sand, and pebbles are frequently utilized due to their strength, stability, and ability to efficiently drain water, which reduces the potential for frost heave and other moisture-related issues. Crushed stone is especially favored for its angular shape, which helps in providing interlocking properties and stability when compacted. Sand is often used to fill voids and aids in drainage, while pebbles can be utilized for their aesthetic appeal in some scenarios.

Wood, on the other hand, does not possess the necessary physical properties to function as a foundational aggregate. It is susceptible to decay, moisture absorption, and does not provide the required load-bearing capabilities or stability that aggregates are supposed to offer. Consequently, wood is not suitable or practical for use in base layers of construction, reinforcing the accuracy of the choice made.